#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main(){
	int n;
	double zi = 2, mu = 1, sum = 0;
	scanf("%d", &n);
	if (n >= 1){
		for (int i = 1; i <= n; i++){
			sum += zi / mu;
			zi += mu;
			mu = zi - mu;
		}
		printf("%.2lf", sum);
	}
	return 0;
}
